On Wed, 3 Jun 92 17:19:34 -0700 cigno at arbaro.esd.sgi.com (Kevin Walsh)
<9206040019.AA17163 at arbaro.esd.sgi.com> writes:
>Re: Maize phloem mass transfer rate
>>I am not a biologist, but have been following the
>thread with interest. Could you post why you
>are doing research on this?
This has been an aside to a study conducted in the field with maize plants.
We occluded 50% and 75% of the peduncle cross-sectional area at either 15
or 30 days post silking (dps) to test whether transport capacity limits
maize grain yield. In order to gain access to the peduncle during the
early grain filling period, it was necessary to remove the ear leaf and
husks of treated ears. Since performing this "preparatory" treatment at
30 dps would have a different effect than when performed at 15 dps, all
plants to be treated (whether at 15 or 30 dps) where "prepared" at 15 dps,
when the first set of treatments were imposed. An additional experimental
justification for removing husks and subtending ear leaf concerns the fact
that husks are modified leaves and are photosynthetically active as well
as important sites of labile assimilate storage. Since we wanted to
measure the effect of transport _to_ the ear, we did not wish to confound
our observations by not controlling internal ear assimilate remobilization.
We know the effect of removing the ear leaf and husks 15 dps (a grain yield
reduction of about 18%) and intended to compare the effects
of vascular flow restriction to this reduced grain yield level.
We observed no yield reduction in these plants that could not be explained
by the "preparatory" treatment. There was also no difference between
plants treated at 15 vs. 30 dps. To explain these results I'm attempting
to estimate mass transfer rates of intact plants and of those we treated.
The purpose is to show that transport rates that are necessary
to sustain normal ear growth with restricted vasculature are indeed
reasonable, and to support the obvious claim that transport capacity of
maize phloem is not a factor limiting grain yield.
I know the daily rate of gain of these ears and hence need only a
reasonable estimate of the phloem sieve tube area through which assimilate
is transported to the ear in order to estimate what the effect on
transport velocity was due to our treatments. Intuitively, it is clear
that in order to sustain ear demand, mass transport rates through peduncles
whose x.s. area was reduced by 50% must have doubled by 2x, and by 3x in
those occluded by 75%. However, I expect that the editors of the journal
where I will try to publish will require more substantial physiological
data in support of our results, which evidently demonstrate, qualitatively
at least, that mass transport rates do not limit maize grain yield.
Ricardo Salvador | Internet: rjsalvad at IASTATE.EDU | "Thou art a little
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